When unsaturated fatty acid ethyl esters contained in liquor are oxidized during storage or by exposure to direct light, an oily smell is produced. In particular, liquor produced by atmospheric distillation contain large amounts of unsaturated fatty acids that are precursors of materials producing an oily smell. When unsaturated fatty acid ethyl esters (especially, ethyl linoleate) are decomposed by oxidation and converted into oily smell components, these components cannot be easily removed from the liquor because they have solubility several thousands times higher than that before decomposition.
Further, higher fatty acid ethyl esters such as ethyl palmitate and ethyl linoleate give a rich taste and mildness to liquor, but on the other hand cause the production of not only an oily smell but also lees. In particular, when such higher fatty acid esters are reacted with metal ions, compounds of unsaturated fatty acids with metal ions are produced as a flocculent precipitate. The metal ions are derived from metals (e.g., copper) used in a distiller.
In order to suppress the production of such a flocculent precipitate, the following method is generally employed: diluting water called “Warimizu” is added to liquor, and the liquor is left standing overnight to produce turbidity and is then filtered to remove turbidity.
However, even when such a method is employed, precursors of materials producing lees cannot be sufficiently removed. This causes a problem that turbidity resulting from fusel oil that is a higher alcohol and/or unsaturated fatty acids occurs when the filtered liquor is further subjected to filtration after storage in a tank or the like. More specifically, such turbidity occurs when the liquor is mixed with water contained in a filter machine so that the alcohol content of the liquor is decreased or when the alcohol in a filter machine is collected by water driving at the end of filtration so that the alcohol content of the liquor is decreased.
Patent Document 1: Japanese Patent Application Laid-open No. H8-322547
Patent Document 2: U.S. Pat. No. 3,007,878
Patent Document 3: Japanese Patent Application Laid-open No. H4-270107